The present invention relates to a manufacturing method of semiconductor devices such as a semiconductor integrated circuit, particularly to a method of forming an element isolation region for dividing an active region into portions for forming semiconductor elements disposed on a semiconductor substrate.
In a conventional manufacturing process of a semiconductor device, a substrate is divided by an element isolation region prior to formation of a semiconductor element onto a semiconductor substrate, so that active regions for the elements are electrically insulated from one another. A shallow trench isolation (STI) system disclosed, for example, in Japanese Patent Application Laid-Open No. 1999-340317 is used in forming the element isolation region.
In the shallow trench isolation system, the semiconductor substrate is subjected to a selective etching treatment using etching masks such as silicon nitride formed on the substrate. A trench is formed in the surface of the substrate by the etching treatment, and insulating materials such as silicon dioxide are deposited in the trench and on the mask so as to fill the trench with the insulating material.
Furthermore, the surface of an insulating layer formed by the deposition is subjected to a flatting treatment by chemical mechanical polish (hereinafter abbreviated as “CMP”). A substrate portion divided by the element isolation region formed in this manner is used as the active region for the semiconductor element.
Additionally, when the insulating layer is formed on the mask, and when there is a certain degree of difference in surface areas of both mask portions with the trench sandwiched therebetween, a shape of the insulating layer deposited on a mask portion having a small surface area becomes steeper. When the CMP treatment is performed on the insulating layer, the steep insulating layer portion on the mask portion having a small surface area is polished more quickly because of a property of a CMP apparatus. As a result, a not local but so-called global stepped portion is generated on the polished insulating layer.
To moderate the stepped portion, according to the prior art, the insulating material remaining on the mask after the CMP treatment is removed. As an example of the removing treatment, plasma etching is performed on the insulating material without patterning the material.
However, in the plasma etching treatment in the prior art, the insulating material in the trench is excessively removed together with the insulating material on the mask in some case. To prevent the insulating material from being partially and excessively removed, a concave surface is formed in the trench. However, the formation of the concave surface obstructs the formation of the element isolation region having a flat surface substantially aligned with the substrate surface in a final flatting treatment process after the mask is removed. Therefore, it is not easy to obtain the element isolation region having a flat surface in the prior art.